The present invention relates to a thermal stabilizer for organopolysiloxane oils. Prior thermal stabilizers for organopolysiloxane oils, which are employed in order to prevent gelation or viscosity increases in the organopolysiloxane oil, have been obtained by a dehydrochlorination reaction in which p-hydroxydiphenylamine is brought into contact with dimethyldichlorosilane or the chlorineterminated dimethylpolysiloxane obtained from dimethyldichlorosilane (refer to Japanese Pat. No. 55-18457[18457/80]).
However, when such a thermal stabilizer is added to an organopolysiloxane oil, the problem rises that the viscosity of said organopolysiloxane oil is reduced when it is subjected to long-term heating at high temperatures.